1. Field of the Invention
The invention is directed to a continuous casting installation and to a process for the production of thin slabs.
2. Description of the Related Art
The use of flat immersion nozzles in continuous casting installations is known, for example, from the prior art reference DE 37 09 188 A1. Further, hydraulically driven lifting platforms which allow the stroke, frequency and mode of the oscillation to be changed and optimally selected by deviating from the sinusoidal oscillation during the casting process itself are conventional. Cambered molds are known, for example, from references DE 41 31 829 A1 and DE 37 24 628 C1. Continuous casting and rolling in which the thickness of the cast metal is reduced during solidification so that the internal quality of the strand is improved is known, for example, from reference DE 38 18 077 A1, among other references.
Evaluation of the prior art reveals that the aim of producing thin strands using continuous casting installation requires the solution of complex problems. The totality of influenceable variables with respect to the entire continuous casting installation is so great that the person of average skill in the art is far from knowledgeable enough, and can also not be expected, to find, from the multitude of more or less usable possible solutions, one solution which will lead to satisfactory results in the most economical manner.
The object of the present invention is to provide a process and a continuous casting installation which make it possible to achieve a given thickness of the thin strand by achieving optimum conditions in the slag supply and in the reduction in strand thickness in the mold and in the guide stand during continuous casting and rolling.
The object of the present invention is met by a process for producing thin slabs or strands by casting molten in an oscillating cambered mold using an immersion nozzle, where the immersion nozzle and mold are sized to meet the condition so that                     F        ST                    F        TA               greater than     50    ,
where FST=the strand cross sectional area of a completely solidified slab and FTA=the cross sectional area of an outlet of the immersion nozzle. The process also includes supplying casting powder to the molten metal such that the height of a slag phase hslag at the upper part of the mold is greater than or equal to the height of a portion of a solid strand shell hstrand-shell which penetrates into the slag phase layer at the upper portion of the mold. In other words, the casting powder is supplied such that the solidified strand shell does not penetrate through the upper surface of the slag phase layer at the upper part of the mold. The oscillation stroke, shape, and frequency of the oscillating movement affect how far the solidified strand shell penetrates the upper surface of the slag phase layer and determine the rate of production of the strand. Accordingly, the rate at which the casting powder is supplied during to achieve the above results is dependent upon the oscillation stroke, shape and frequency of the oscillating movement of the mold because these parameters determine the rate at which the strand is produced. A faster production of strand requires a faster rate of supplying of casting powder. The strand which leaves the mold is then reduced directly below the mold in a plurality of steps in a cluster roll stand so that the strand achieves its final thickness while still having a liquid core at the end of the cluster roll stand. The solidification is controlled so that a two-phase zone is present within the strand after achieving the final thickness at the output of the cluster roll stand.
In a further embodiment of the present invention, casting powder which facilitates the formation of slag in the cast surface is supplied so that an active thickness in the cast surface is constant along the entire thickness of the slab.
In another embodiment, both the oscillation characteristics of the mold and the invention, the mold is configured so that the longer pair of sides of a strand exiting the mold outlet comprise a camber such that the sides are slightly curved instead of being flat. The curve is symmetrical about a center axis of the strand. The curved sides produce a difference between the thickness of the strand at the ends of the side and thickness of the strand through the center of the side. This difference in thickness produced by the curved sides is less than 4% of the of the final thickness of the strand.
The object of the present invention is also met by a continuous casting installation including an oscillating rectangular mold and means for oscillating the mold, the means for oscillating the mold being adjustable relative to frequency, stroke and mode of oscillation. The invention casting installation also includes an immersion nozzle arranged to project into the rectangular mold having a cross sectional area that is less than {fraction (1/50)} of the cross sectional area of the completely solidified slab or strand. The casting installation further includes means for supplying casting powder to the mold as a function of the stroke, mode, and frequency of oscillation of the oscillating mold such that the height of the slag phase layer formed at the upper end of the mold is greater than the height of the strand shell which penetrates the slag phase layer. A cluster roll arranged downstream of the mold and includes two rolls that are adjustably arranged at a distance from one another. The cluster roll further includes a hydraulic arrangement operatively arranged for continuously adjusting the distance between the two rolls.
In another embodiment of the present invention, the mold is configured so that from the cast surface to the mold outlet, the thickness of the mold never exceeds 120% of the thickness of the strand at the mold outlet.
In a further embodiment, the two rolls are arranged to have a distance therebetween for reducing the strand thickness as the strand is fed through the rolls. The reduction in thickness reduces the area of the of the liquid interior and therefore creates a flow of the remaining liquid. The flow results in a stirring effect in the remaining liquid interior of the strand with a predetermined strand thickness reduction.
The solution to the problem is not dependent upon the type of mold, e.g., vertical mold, vertical mold with bend, or curved mold.
The invention is described hereinafter by way of example with reference to the drawings.